Bell nipple monitor

ABSTRACT

A method and apparatus for use in warning of changing conditions in a well during the drilling thereof consisting of determining differences in the hydrostatic head of the drilling fluids in the bell nipple above the flow line and recording the hydro static pressure to give a continuous record of changes during normal drilling operations. The apparatus consists of an air conduit connected to a bell nipple through an orfice in the bell nipple below the flow line. The air conduit communicates with a source of compressed air which is supplied with an air regulator for the purpose of maintaining a constant pressure source. Changes in hydrostatic head of the drilling fluid above the orfice is continuously detected by changes in the pressure in the air conduit and these changes are continuously recorded and correlated to reflect mud volume changes in the drilling fluid from the well.

United States Patent 1191 Rochon et a].

[ Aug. 6, 1974 BELL NIPPLE MONITOR [57] ABSTRACT [75] Inventors: Robert Rochoni Joe Sneed A method and apparatus for use in warning of changboth of San Antomo ing conditions in a well during the drilling thereof con- 7 Assignee; Monarch Logging Company Inc sisting of determining differences in the hydrostatic San Antonio head of the drllllng fluids 1n thebell nipple above the flow line and recording the hydro static pressure to [22] Flled: June 29, 1972 give a continuous record of changes during normal [21] APPL 268,187 drilling operations. The apparatus consists of an air conduit connected to a bell nipple through an orfice 1n the bell nipple below the flow line. The air conduit [52] US. Cl. 73/155 Communicates with a source f compressed which o "1.... an air for [58] Field of Search 73/151, 152, 155, 299 maintaining a constant pressure: Source Changes in hydrostatic head of the drilling fluid above the orfice 1 1 References Cited is continuously detected by changes in the pressure in UNITED STATES PATENTS the air conduit and these changes are continuously re- 2,340,993 2/1944 Smith 73/155 Corded and correlated to reflect mud volume Changes 2,832,566 4/1958 Bielstein. 73 155 x in th drilling fluid r m t l- 3,161,051 12/1964 Perry, .1r. 73/299 3,760,891 9/1973 Gadbois 73/155 X Primary Examiner.1erry W. Myracle Attorney, Agent, or f rm1CQx s ithaSmimalia e Guenther Incorporated ill! 1 Claim, 2 Drawing Figures 7d 2 LI .W.

PATENTEB RUB 61974 F/GIZ BELL NIPPLE MONITOR BACKGROUND OF THE INVENTION This invention relates to a means for determining with great accuracy, changing conditions in the bore hole during the drilling of a well in the quest for hydro carbons and recording the changes at the time of occurance. During the drilling of a well in the quest for hydrocarbons using the rotary method of drilling, a fluid termed drilling mud is circulated down through the drill pipe and up through the angular space between the drill pipe and the well bore.

The drilling mud is ssential to a well drilling operation as it serves to carry away the cuttings from the bit to facilitate drilling and it opposes the force of the formation pressure from below to prevent blowouts; additionally, it serves as a medium which transports the cuttings from the drilling bit out of the well bore to be separated from the mud by a shaker or settled out in a mud pit at the top of the well prior to recirculation. The mud also cakes on the surface of the well bore and resists caving of the side walls of the bore hole and seals the bore to prevent the drilling mud flowing out into the porous formation material.

It is necessary that the drilling mud be of sufficient weight to balance against the force of any upwardly acting hydrostatic pressure such as the pressure of gas, water, or oil which may be exposed in drilling, and at the same time the drilling mud should not become so heavy that it enters the formation causing a loss of circulation. As conditions encountered vary in the course of drilling, the weight of the drilling mud has to be varied constantly to meet these changing conditions. For instance, if a gas sand is penetrated the gas in the pore space will become a part of the drilling fluids. As the fluids are pumped out of the hole and the gas expands, mud flows out of the hole at a faster rate than it enters. Such a condition must be detected immediately as remedial action may be necessary by the addition of weighting material to the mud or otherwise the mud might not contain the force of the formation pressures reacting upwardly thereagainst with the consequence that a blow-out may occur.

The use of excessive mud weight to provide a large factor of safety against blowouts was previously used as standard drilling procedure. With the advant of a new drilling concept of balanced pressure drilling, it became essential that continual accurate measurement of the mud density be maintained at all times during the drilling operation. Balance pressure drilling grew out of the need for more economy in the drilling operation, since less dense mud allows faster drilling with less wear on the equipment. In order to accomplish this, the factor of safety resulting from excess mud weight had to be reduced substantially. To offset this reduced factor of safety, it was imperative that fluid gain or loss and gas expansion in the mud system be noted as soon as possible. Of course the best evaluation of bottom hole conditions isto continuously and accurately measure changes in the volume of mud flowing out of the hole. Such a determination will provide information essential to warning that a change of mud volume out has taken place. This change when not associated with changes of mud volume being pumped into the hole is associated with bottom hole conditions.

An apparatus adapted for use in the detection and quantitative analysis of gas and the measurement of the volume of gas per minute entering the hole during the drilling of a well is disclosed in a pending application of Robert W. Rochon, Ser. No. l64,530, now abandoned, filed on June 21, 1971, one of the co-inventors of this invention. Although this information is important it is after-the-fact information since it is a measure of the volume of gas in the drilling mud at the surface. The forewarning apparatus ofthe present invention will detect the presence of gas in the bore hole before it reaches the surface and thereby allow precautionary measures to be taken such as increasing the mud weight or shutting the well in.

Drilling for hydrocarbons is hazardous as evidenced by frequent blowouts which cause considerable air and water pollution and general ecological damage. Blowouts result from the unknown relationship between formation pressures and the weight of the drilling mud which is pre-determined to contain the formation fluids consisting of gas, oil or water. Many devices have been developed to give advance warning of potential trouble so that remedial action may be taken to minimize the trouble and control the well. The basic pre-warning and indication of trouble is the relationship between the input mud weight and the output mud weight. if the volume of the returning drilling fluid is less than that of the input drilling fluid, the formation is taking drilling fluids. This is the beginning of a very serious condition of loss of circulation in which mud enters the formation faster than it is being pumped in. The sooner this condition is determined, the easier it is to seal off the zones taking fluids. The lowering of the hydrostatic pressure of the mud by lowering of the mud column may cause formations which were previously contained to start producing and the well to blow out. If more mud comes out of the hole than is pumped in, fluids are entering the hole. When fluids enter the hole, mud containment pressures are inadequate. Any addition of fluids will compound this under-balance. Salt water entering the well from the formation will mix with the heavier mud and lighten the weight of the column as the mixture is pumped out of the well. Trouble is compounded with time as the rate of flow increases as the unbalance condition becomes more pronounced. Fluids in the formation represent energy. Now if the degree of unbalance is sufficient and permeability of the reservoir which is directly related to the energy deliverability of the formation is great enough, the entire mud column may be lifted off the bottom. The optimum time for precautionary measures is at the time initial lift or kick. The amount of the reservoir opened is. kept to a minimum and the pressure differential will be at its lowest when there is a full column of mud in the well bore. The danger of an unobserved lift or kick increases expotentially as a function of time. All of the aforementioned conditions are immediately reflected by a change in the height of the mud column in the bell nipple above the flow line.

If the well is over balanced, the expansion of gas which has been drilled up will take place in the top 10 percent of the hole, however, if the well is under balanced it will occur at a greater depth depending on the degree of under balance. When the gas expands it will force an amount of mud out of the hole equal to the volume of the expanded gas thus the volumne of the exit mud is increased by this amount. The method and apparatus of the present invention is intended to measure the initial kick" at the time of the initial entry or expansion of the gas rather than waiting for the expansion to be visibly noticable. Since the initial kick will be reflected as a very slight change in the height of the mud column, it is imperative that the apparatus be sensitive to very minor changes in the height of the column. The present invention will continuously record changes in the hydrostatic head of the mud in the bell nipple above a point slightly below the flow line. Early detection of the initial small changes in the mud volume out of the well before it becomes visibly apparant in the essence of well safety.

Presently there are two pre-warning devices which are commonly used to determine changes in the volume of mud flowing from a well. These are a pit volume indicator and a flow line device, both of which are used to detect changes of flow during the drilling of a well. The present invention adds another parameter to the present pre-warning systems. A reliable pre-warning system is important because of the probability that no one piece of equipment will operate without breakdown and its importance warrants several dimensions of information, even including duplication. Furthermore, the prior art devices are incapable on some drilling rigs of the degree of sensitivity of measurement which can be accomplished with the present invention. For example, the pit level indicators are inadequate because they operate to reflect changes in the level of the mud pit which occurs over a relatively large surface area and changes in height per increase in unit volume is very slight. The performance of the flow line devices must depend on the physical configuration of the drilling rig, therefore uniformity becomes rather difficult. Most flow line devices depend on a mechanical flap type arrangement which is activated by the flow of fluids across the flap to in turn signal a recording device or other gauge.

One type of apparatus for determining changes in the height of the column of mud is disclosed in U.S. Pat. No. 2,340,993. The apparatus disclosed in this patent includes a stand pipe communicating with the flow line and extending upward therefrom parallel to the well casing. Changes in elevation of the mud in the well casing will cause a corresponding increase in the elevation of the mud standing in the stand pipe which can be measured by a suitable measuring device. Of course, the apparatus must be provided with a flow line having an upward slope to insure that a full pipe of mud is always provided at the point where the stand pipe is connected to the flow line. A disadvantage of this apparatus is that no accurate measurement can be made of the height of the mud in the well casing if the height falls below the upper surface of the flow line. Another typical flow line device is disclosed in U.S. Pat. No. 2,832,566. This patent also discloses a pressure sensitive device for reflecting changes in the weight of the mud column by balancing a column of air against the column of fluid in the well casing. Changes in the air pressure required to balance changes in the weight of the mud column are used to determine the weight of mud to be added to the drilling fluid to maintain a normal drilling mud weight. The location for the introduction of the pressurized air into the well casing is located at a depth of 25 to 75 feet below the surface which location renders the apparatus impractical for use as a sensitive forewarning device where slight variations in the height of the mud column are significant.

Much of the present and immediate future exploration for hydrocarbons will be in offshore areas where the wells are very deep and the gas pressures are abnormally high and the waters of the shales arefgassaturated. Blowouts in the high pressure deep wells has resulted in air and water pollution of tremendous consequence and it is a primary object of this invention to provide a method and apparatus that is capable of giving an early warning of conditions occuring in the bottom of the well, at the time of the occurance, to afford ample time to initiate preventative action and thereby lessen the risk of blowouts.

SUMMARY The present invention contemplates measuring changes in the height of the column of drilling mud in the bell nipple with great precision and accuracy. This is accomplished in part by introducing air at a constant pressure through a conduit into the bell nipple at a location immediately below the bottom of the flow line. The air is introduced at a constant volume and pressure and changes in the hydrostatic head of mud above the point of introduction of the air acts to change the force acting against the constant air supply which canges the pressure in the air supply conduit which pressure is transmitted to a recorder. The pressure is correlated with hydrostatic head in inches and the recorder records the information as hydrostatic pressure of the mud in the bell nipple.

The apparatus to accomplish the purpose of this invention consists of an orifice in the bell nipple just below the bottom of the flow line. A pipe collar is welded into the bell nipple at the orifice on a 45 angle. A nipple, pipe and plug combination is screwed into the collar. An air conduit is connectedto the pipe and communicates with an air supply source. An air regulator is connected to the air supply conduit to regulate the air pressure in the air supply conduit. A flow meter is also provided in the conduit to limit the volume of air and to minimize drying of the mud in the end of the pipe where the air flows into the bell nipple. The air supply conduit is further provided with a recorder to continously record variations in the pressure in the air supply line caused by variations in the height of mud i the bell nipple.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of the casing going into a well with the bell nipple mounted thereon.

FIG. 2 is an elevation view partly in section showing the apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As can be seen from FIG. 1, a bell nipple 1 may be mounted on top of a blowout preventer 2 which is in turn mounted on top of easing 3 in known manner. The casing exits from a hole 4 in the ground 5. It will be understood, however, that the casing 3 will extend further from the surface of the ground depending upon the location of the drilling operation as for example in offshore drilling operations.

Referring now to FIG. 2, the bell nipple l is shown having an outlet opening 7 communicating with a sloping flow line 8. Flow line 8 communicates with a mud pit (not shown). The bell nipple is open at its upper end 9 for receiving drill stem 10. The bell nipple is open at its lower end 11 so that mud returning from the well can pass upward therethrough. An orifice 12 is provided in the wall 13 of the bell nipple at a point slightly below the flow line opening 7. A pipe collar 14 is connected to the bell nipple at the orifice 12. The pipe collar 14 is preferably mounted at a 45 angle to the bell nipple 1 so that it will be self-draining. A 45 ell 15 is connected to the pipe collar 14 to complete a 90 turn. A reducer 16 connects the 45 ell 15 through a union 18 to air supply conduit 17. Air supply conduit 17 communicates with an air supply source 20. Mounted inside the collar 14 and the ell 15 is a Teflon pipe 19. The Teflon pipe 19 is in communication with the air supply conduit 17. The Teflon pipe 19 is held in position by the frictional engagement with the bend inside the 45 ell. One means which has been found satisfactory is to bend the Teflon pipe 19 at a greater angle than 45 ell 15 so that the Teflon pipe will wedge against the bend in the ell 15 at a point 22. An air regulator 23 is connected in the air supply conduit 17 to regulate the air pressure flowing through conduit 17 and into the bell nipple 1. A pressure gauge 24 is provided so that the pressure in conduit 17 can be accurately set. A flow meter 25 is also connected in conduit 17 to limit the volume of air flowing through the conduit and to the bell nipple 1. This regulated flow reduces the air friction in the air supply conduit 17 thus increasing the accuracy. Still another reason for regulating the flow through air conduit 17 is to limit the amount of air passing out through the Teflon tube 19 which has a drying effect on the mud thus causing caking within the Teflon pipe 19. The lower the air flow rate, the less drying effect it will haveon the mud inside the Teflon tube 19. It is very important that the air supply from the conduit 17 into the bell nipple 1 be maintained uniform at all times thus the need for the Teflon pipe 19. This will prevent caking of the mud on the Teflon even if the mud is dried by the air flow through the conduit. The dried mud is merely flaked off of the Teflon pipe 19 and flows back into the mud stream inside the bell nipple 1, thus assuring that the air supply to the bell nipple 1 is always open. Asuitable recorder such as a clock recorder 26 is mounted in the air supply conduit 17 between the bell nipple 1 and the air regulator 23. The recorder 26 continuously records air pressure in the conduit 17. The air regulator is set to maintain the pressure in the air supply conduit 17 at slightly greater than the hydrostatic pressure of the mud in the bell nipple. The hydrostatic head H is the normal height of the mud in the bell nipple during normal drilling operations. Any changes in the head H due to entrained gas in the mud, loss of mud to the formation, gas kicks or any of the other previously discussed factors, will be reflected on the recorder 26 due to the increase or decrease in the pressure in the conduit 17 because air discharging through the Teflon pipe 19 is operating against the hydrostatic head H which determines the amount of air pressure in the conduit 17. Very slight variations in the hydrostatic head H will be recorded on the recorder 26.

A high pressure alarm switch 28 and a low pressure alarm switch 29 may also be mounted in the air supply conduit 17 to give a warning signal in the event of a pre-determined increase in the hydrostatic head H or a decrease in the hydrostatic head H.

As can now be seen from the foregoing description a very reliable and accurate apparatus has been provided to warn of changes in the mud volume flowing out of the well during drilling operations. During normal drilling operations with the well in an overbalanced condition the mud volume in is substantially equivalent to the mud volume out of the well. The normal hydrostatic head H is determined for this condition and the air in air supply conduit 17 is regulated by the air regulator 23 to be slightly greater than the pressure of the hydrostatic head H. Any variations in the hydrostatic head H will be reflected as a change in the pressure in the air supply conduit 17 and thus instantly be recorded on the recorder 26 as a change in. mud height. This information is very accurate due to the location of the outlet of the Teflon pipe 19 to the normal upper level of the mud standing in the bell nipple l. Slight variations which might be caused by gas kicks will be reflected as a slight increase in the hydrostatic head H. As previously discussed, this slight variation may be a reflection of a substantial inflow of gas which has just started to expand in its travel up the hole. The warning comes at the time of the kick and it is not necessary to wait for substantial expansion to occur. The apparatus described herein is suitable for use on all wells regardless of the shape of the flow line because the air conduit delivers the air to the bell nipple slightly below the lower level of the flow line. This enables the flow line to be sloping for self-draining since the apparatus is not dependent upon the shape of the flow line to maintain a head of mud above the discharge end of Teflon pipe 19.

Having now described a preferred embodiment of my invention what I claim is:

1. A method of rapidly detecting gas expansion and fluid flow in a well during drilling operations consisting of a. introducing a constant supply of air at a constant pressure into the mud column in the bell nipple at a point immediately below the bottom of the flow line,

b. continuously recording changes in the hydrostatic pressure of the mud column acting against the air supply, and

c. determining conditions in the well by correlating the changes in the hydrostatic pressure of the mud column to changes in the height of the mud column in the bell nipple to determine that conditions in the well have changed to influence the height of the mud column. 

1. A method of rapidly detecting gas expansion and fluid flow in a well during drilling operations consisting of a. introducing a constant supply of air at a constant pressure into the mud column in the bell nipple at a point immediately below the bottom of the flow line, b. continuously recording changes in the hydrostatic pressure of the mud column acting against the air supply, and c. determining conditions in the well by correlating the changes in the hydrostatic pressure of the mud column to changes in the height of the mud column in the bell nipple to determine that conditions in the well have changed to influence the height of the mud column. 